The present invention relates to small motors and methods of making the same and, more specifically, to a structured product family of motor models that utilize a maximized number of common, optimized, multiple application, cost minimized, components in a cost minimized manufacturing process for utilization in a plurality of different applications, including automotive applications.
Traditionally, in industries using electric motors such as for example the automotive industry, each specific motor application required a considerable number of individual components with few, if any, common components between applications. For example, there typically were different motors for each model of automobile and within automobile models, there typically were different motors for heater only blower systems or air conditioning blower systems and for front wheel drive models as well as some rear wheel drive models, there was typically a different motor for the radiator cooling fan.
One specific example of this in the automotive industry was the practice of utilizing three components for the motor frames, a base component, a rear end shield component, and a combined unitary front end shield-mounting flange component. This particular practice resulted in separate tools for each different end shield-mounting flange integral combination for each application which required a different axial position of the mounting flange relative to the motor frame. Tools for the combined integral end shield-mounding frame were quite expensive.
Thus, at least one major automatic manufacturer, it was conventional to have nearly as many sets of motor manufacturing tooling as there were different motor applications. This conventional system was wasteful of resources in that it required repetitive, short duration production runs using a plurality of tooling, thereby raising the unit cost of producing the required number of different motors to an unacceptable level.
Thus, in order to reduce costs and manufacturing complexities, it is desirable to develop a "structured product" motor having a minimized number of total components which with minor component and manufacturing variations could be used to produce motors for a maximized number of different automotive applications that are capable of operating with minimum noise, highly durable, and have substantially lower unit production cost.
The brush assembly plates for motors and generators alike vary in design, but in general comprise boxes to house the brushes, spring means to apply pressure to the brushes to urge them against the commutator, electrical leads to provide a current path to the brushes and a mounting surface holding these elements that also provides a means to secure the entire assembly to the motor in such a manner as to place the brushes in a proper working relationship with the commutator.
The useful life of electrical motors that typically find applications in appliances, tools, and automotive vehicles, as well as many industrial applications, is usually a function of the length of the carbon brush, brush rate of wear, and, in the case of replaceable brushes, the number of times the brushes can be replaced before the commutator begins to severely wear.
It is known that the rate of wear of the brushes is a function of the load, the speed of the motor, and more importantly, the spring pressure that is applied to the brush to keep it in bearing contact with the commutator. Accordingly, it will be appreciated that with too much spring pressure, the mechanical wear of both the brush and commutator will become excessive, a film having undesirable characteristics is formed on the commutator, and the brush life markedly falls. On the other hand, with too little pressure applied, the electrical arcing due to the high contact resistance and the mechanical abrasion due to brush and commutator surface bounce greatly reduces potential brush life by destroying the brush and the commutator surface.
A typical automotive motor brush configuration comprises a helical spring bearing on the carbon brush, the two elements being contained in a box-like holder such that the brush is urged against the commutator. Although this design is commonly utilized, it has limitations. Specifically, the pressure produced by a helical spring is a function of its compression or extension. Therefore, when the brush assembly is new, and the brushes are at their maximum length, the spring is at its fullest compression and the pressure therefore is at its highest. At the end of the brush life, the spring extension is at its greatest and the pressure now on the commutator is below that desired. Therefore, depending on the spring rate, only a portion of the brush wear is in the optimal spring pressure range.
The conventional motor brush spring used in automotive applications tends to have a nonconstant force. In other words, the harder and the further you pull the spring back, the harder it pushes on the resistance. Thus, if the spring is moved a short distance from its normal at rest position, there will be a relatively lower force generated by the spring against the resistance. The further you move the spring away from its at rest position, the greater the force exerted by the spring against the moving force. However, in applying pressure to brushes on a brush box assembly plate, it is desirable that a constant force be exerted against the brush urging the brush against the commutator throughout the life of the brush and especially after initial wear in.
An additional problem with conventional motor brush springs in automotive applications is the space they occupy. Specifically, there is only so much space available within the motor frame to house all of the motor components. Conventional spring means such as coil springs take up valuable space in the brush area.
With regard to a conventional helical spring which has a finite collapsed length and which is generally enclosed in the brush box located behind the brush, the space required by the collapsed spring necessitates that a shorter brush per length of brush box be used.
Thus, it is desirable that a spring means be developed which not only develops a rather constant force, but also occupies minimum space in order to allow the brush sizes to be increased and increase the life of the motor.
In certain applications, in order to overcome these shortcomings, a ribbon spring that is essentially wound like a clock spring and is set to unwind in such a direction as to hold the brush against the commutator has been utilized. Since ribbon springs have an essentially constant force, the ideal pressure range can be obtained thereby obtaining optimum contact between the brush and the commutator throughout the life of the brush.
With the ribbon spring, the coils providing the engaging force are mounted outside of the brush holder on either side thereof and hence only a thin ribbon section of the spring is located in the brush box behind the brush. Consequently, this configuration provides extra space for a longer brush and hence results in the much desired longer brush life.
However, problems have arisen with brush box/ribbon spring designs in that occasionally erratic brush life results due to the fact that the walls confining the spring coil portions tend to impede brush movement in the box perhaps because of vibration in the back and forth motion of the brush and the unwinding rotation of the coil portions. Brush impediment may also be due to the coil portions riding back and forth, or in and out, as well as dereeling in their receptacles.
It is known and appreciated that it is essential that the brush follow the commutator at all times. However, no matter how well or fine the commutator, the shaft, and the bearing surfaces are machined, some eccentricity will remain in the motor. Accordingly, it is very important to maintain not only the spring pressure, but also a large degree of freedom of movement of the whole system connected to the brushes.
With conventional designs utilizing ribbon springs, there is a tendency for the brush to hit the brush box wall and drag on the bottom or floor thereof. Accordingly, debris such as carbon, dust and the like tends to be deposited in these areas which further tends to reduce the freedom of the system to move.
Brush boxes designed to overcome these shortcomings, such as those disclosed in U.S. Pat. No. 4,800,313 to Warner et al., involved the arrangement in which the outer wall of the receptacle or brush box was eliminated and at least two semicircular surfaces were provided for establishing point or line contacts with each ribbon spring coil portion.
While this system did somewhat solve the difficulties involved with the application of the ribbon spring design, a need still remained for a simplified brush box ribbon spring system which: would increase the brush life by providing the essentially constant force of the brush on the commutator once the entire brush was in contact with the commutator; would virtually eliminate the tendency of the brush to become hung up in the brush box due to debris, such as residue, carbon, dust and the like; and keep the coils of the ribbon spring relatively free to rewind toward their at rest conditions without binding or being impaired by any component of the brush box or the debris from the system as the brush wears against the commutator.
One of the popular brush plate designs, especially for small fractional horsepower motors, utilizes a molded brush plate member of a one-piece construction formed from a high temperature resistant plastic which is electrically nonconductive. The member has the brush boxes formed thereon as well as various openings for securing it to the motor housing and for receiving an extending armature shaft having a commutator secured thereto.
A source of noise in the conventional automotive small electric motor has been the brush. Specifically, the interaction between the brush and the commutator has generated a considerable amount of noise because of the shape of the brush itself. Specifically, one source of noise is the edge of the brush catching in the commutator slots, thus not only resulting in noise, but also in momentary increases in the current density as the brush skips a little over the commutator when the brush is caught in the slot.
An additional source of noise in the conventional electric motor has been transmitted through the brush box assembly plate to the frame. Specifically with a rigid connection between the plate and the frame, vibrations generated between the brush and the commutator transmitted to the plate and then to the frame have produced an unacceptable level of noise in the conventional design.
Thus, it is desirable to develop a connection between the brush assembly plate and the frame which reduces and isolates the vibrations generated by the brush commutator interaction and which are transmitted to the frame.
Generally, in prior bearing systems utilized in motors for automotive applications, automatic self-aligning bearing material which is held under the effect of resilient force by allowing a plurality of pawls formed on a metal holder or retaining plate to come in pressure contact with the outer peripheral surface thereof has been employed. It is known that the alignment torque required for the purpose of self-aligning of the ball metal increases correspondingly as resilient force on the pawls increases. Accordingly, it is preferable that the resilient force of the pawls be reduced in order to assure that automatic self aligning is effected smoothly.
However, when the resilient force of the pawls is reduced, they cannot satisfactorily oppose a load exerted on the ball metal in the radial direction or in the axial direction, resulting in a nonreliable supporting function being maintained. Thus, it is preferable that the resilient force of the metal holder be kept low in order to have a reduced alignment torque, while it is also preferable that it be kept high in order to satisfactorily oppose a load exerted on the ball metal. Accordingly, the resilient force of the metal holder is required to have two contradictory characteristics. However, since the conventional metal holder was so constructed that each of the pawls had the same resilient force, it couldn't have both the high and the low resilient forces required.
In view of the above, the existent state relative to the metal holder is such that reliable shaft support is considered first and the function of smooth self-aligning is somewhat sacrificed. Consequently, the alignment torque required for the ball metal is increased and thus the desired self-aligning cannot be easily achieved. Another drawback is that when the metal holder is so fitted that the pawls have a predetermined resilient force, it has a narrow range of adjustment and satisfactory fitting is achieved only with much difficulty.
Other attempts to overcome these shortcomings have included providing a holding device for an automatic self-aligning ball metal of which the outer peripheral surface is spherical, the ball metal being adapted to be held by means of metal holder, wherein the metal holder is formed with at least two kinds of pawls having a different intensity resilient force. The pawls having a lower intensity of resilient force come into contact with the outer peripheral surface of the ball metal earlier than those having a higher intensity of resilient force in order to resiliently hold the ball metal.
The pawls extend in the radial direction inwardly of an area located in the proximity of the outer periphery thereof. The pawls having a lower intensity of resilient force and the pawls having a higher intensity of resilient force are alternately arranged in the peripheral direction of the metal holder.
Usually the pawls having a higher intensity of resilient force have a width wider than those having a lower intensity of resilient force. Alternatively, the pawls having a higher intensity of resilient force may be thicker than those having a lower intensity of resilient force on the assumption that they have the same width.
Bearing retainers constructed in the above described later developed manner whereby the resilient holding force exerted on the bearing by the retainer functions weakly at the time of automatic self-aligning, but functions intensely when there's a load applied to the ball metal in the axial direction, are shown in U.S. Pat. No. 4,806,025, issued Feb. 21, 1989, to Kamiyama, et al. While the automatic self aligning bearings described in the above patent were advances over the known art, solutions to the problems of repeatability and the amount of force required to align the bearings have remained elusive.
In conventional motors having permanent magnet field poles, reluctance torques are introduced during rotation of rotary errantries under the poles. The reluctance torque is a position-sensitive periodic-with-rotation torque which occurs in the absence of excitation of the armature. Occurrence of this torque is due to the interaction of the permanent magnet field and the slots in the armature. Because of these slots, the reluctance of the magnetic flux varies at different points around the armature. This means that the magnetic energy in the air gap field between poles and the armature is not uniform at all points circumferentially around the armature. This occurrence of reluctance torque is manifested by pulsations, throbbing and irregularity in rotational speed which are objectionable at all rotational speeds, but are most noticeable and objectionable at low speeds. Previously, attempts have been made to reduce reluctance torque in direct current motors by such means as for example skewing the armature slots. However, skewing adds complexities to the armature manufacturing process.
The reluctance torque phenomenon occurs inherently in all energized motors which have a change in the air gap as a function of rotation. It is desirable to control reluctance torque especially in automotive applications while minimizing the number of different components necessary to accomplish the maximum number of applications and minimizing product and process cost and complexities.
Another problem with prior conventional motors, especially those utilized for automotive radiator cooling applications, has been durability. Specifically, one motor design failed after approximately 500 hours of usage which roughly corresponds to 40,000 miles of automobile driving. These prior motors failed primarily because the motor brushes had been used up. Thus, in order to extend the useful motor life used in such an application, it is desirable to extend the brush life.
Another determined shortcomings of this prior motor utilized as a radiator cooling motor was bearing failure possibly due to bearing lubrication failure. Thus, it would be desirable to develop a lubrication system or a bearing system for the motor which extended the life of the bearing systems.
Accordingly, there is a need for an improved motor and methods of making the motor and its various components. Such a motor should be a structured product utilizing a minimum number of components to accomplish a maximum number of different applications including automotive applications and should: produce significantly reduced noise levels in comparison to prior motors especially those for automotive applications; have a predetermined set of conditions preset in at least one bearing system which is repeatedly duplicatable in a plurality of other individual bearing systems; have an improved brush card assembly; have precisely contoured and beveled brushes which significantly reduce the noise produced by the brush/commutator interaction; have precisely dimensioned and aligned brush boxes; have a brush box/brush plate combination which significantly reduces stresses in the plate; have the laminations assembled to the shaft such that a minimum amount of stress is applied to the shaft; have a commutator assembled to the shaft such that a minimum amount of stress is applied to the commutator itself or to the shaft; have an armature which is first rough finished, balanced, and then final finished to insure precise dimensional tolerances balance; have oil slingers which are part of the armature; have a stiff end shield which reduces the noise produced by the motor; have precisely designed and contoured magnets and precisely designed laminations whose interaction reduces reluctance torque; and have an adhesively mounted flange/frame combination which significantly reduces the noise produced by the motor and reduce tooling costs.